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Mitochondrial and alpha-proteobacterial time of divergence - a question of antecedence
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolution, Genomics and Systematics, Molecular Evolution. (Siv Andersson)
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolution, Genomics and Systematics, Molecular Evolution.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolution, Genomics and Systematics, Molecular Evolution. (Siv Andersson)
(English)Manuscript (Other academic)
Abstract [en]

Mitochondria are believed to have originated by the incorporation of an alpha-proteobacterium into an un-defined "proto-eukaryote", although the exact nature of the two participants in this endo-symbiotic event is not known. Attempts to place the endo-symbiont with a specific group of extant alpha-proteobacteria has in most cases identified the Rickettsiales as the sister-group to mitochondria, although recent work has shown that this could be due to methodological artefacts and that the mitochondria should instead be considered a sister-clade to alphaproteobacteria. Equally uncertain is the time at which this endo-symbiotic event took place, and if it coincides with the event that gave rise to the eukaryotes themselves. In this work we attempt to use molecular dating methods to compare the time-point of mitochondrial divergence to the time-point of divergence of the alpha-proteobacteria, under the two hypothetical topologies mentioned. We show that if mitochondria are considered as a sister-clade to the alpha-proteobacteria, mitochondria likely diverged prior to the radiation of extant alpha-proteobacteria, and that the alpha-proteobacterial clade itself might be significantly younger than shown in previous analyses.

National Category
Biochemistry and Molecular Biology
Research subject
Molecular Biology
Identifiers
URN: urn:nbn:se:uu:diva-100845OAI: oai:DiVA.org:uu-100845DiVA: diva2:211106
Available from: 2009-04-08 Created: 2009-04-08 Last updated: 2010-01-14
In thesis
1. Mitochondrial and Eukaryotic Origins: A Phylogenetic Perspective
Open this publication in new window or tab >>Mitochondrial and Eukaryotic Origins: A Phylogenetic Perspective
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Mitochondria are eukaryotic cellular organelles responsible for power-generation, believed to have come into existence by an endo-symbiontic event where a bacterial cell was incorporated by an un-specified "proto-eukaryote". Phylogenetic analysis have shown that the mitochondrial ancestor was most related to present-day alpha-proteobacteria, although the exact nature of the mitochondrial progenitor remains disputed.

In this work, I have used phylogenetic and other methods to investigate the identity of the organism giving rise to mitochondria, by analysing the evolutionary history of select proteins, the events where they have been transfered to the eukaryotic nucleus, and the time-point of mitochondrial establishment. In addition, a search for mitochondrially related organisms in the ocean metagenome was performed, in the hope that something more related to the mitochondrial progenitor than anything previously identified could be found.

Previous analysis have shown that a large fraction of mitochondrial proteins does indeed trace their descent to the alpha-proteobacteria, but I found that the amino-acyl tRNA-synthetases display more general bacterial descent, making it likely that these proteins are of a different origin from the mitochondria themselves.

While the synthetases are encoded on the nuclear genome, most mitochondria still posses most of the tRNA on their own genomes. In the cases where the tRNA has been lost from the mitochondrial genome, I found that the probability of loss correspond to the evolutionary history of their synthetase.

The ocean metagenome represents an order of magnitude more data than previously available, making it suitable for improving the analyses dealing with mitochondrial placement. This large of amount of data was utilised to improve the phylogenetic analyses, showing that previous works might have suffered from artefacts inflating the support for placement of mitochondria with a specific alpha-proteobacterial group.

Eukaryotic/mitochondrial radiation was shown to be as old, or older, than radiation of extant alpha-proteobacteria, casting doubt on previous analysis identifying a specific alpha-proteobacterial group as the mitochondrial ancestor.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2009. 51 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 637
Keyword
Molecular evolution, Phylogenetics, Mitochondrial origin and Evolution
National Category
Biochemistry and Molecular Biology
Research subject
Molecular Biology
Identifiers
urn:nbn:se:uu:diva-100147 (URN)978-91-554-7507-9 (ISBN)
Public defence
2009-05-20, Lindahlsalen, Evolutionsbiologiskt centrum, Norbyvägen 18, 75236 Uppsala, 13:00 (English)
Opponent
Supervisors
Available from: 2009-04-28 Created: 2009-03-26 Last updated: 2009-05-04

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